The development of solid cleaning compositions has revolutionized the manner in which detergent compositions are manufactured, dispensed and used. Solid block compositions offer unique advantages over the conventional liquids, granules or pellet forms of detergents, including improved handling, enhanced safety, elimination of component segregation during transportation and storage, and increased concentrations of active components within the composition. Solid block cleaning compositions, such as those disclosed in Fernholz et. al., U.S. Pat. Nos. Re 32,763, Re 32,818, and Heile et al., 4,680,134 and 4,595,520, have quickly replaced many of the conventional composition forms in commercial and institutional markets.
Urea has been used in cleaning and sanitizing compositions as a hardener and solubility modifier in organic rinse aids, as described for example in Morganson et al., U.S. Pat. No. 4,624,713. Morganson et al. teach that urea can be combined with polyalkylene oxide polymers to form solidification complexes known as inclusion compounds. Urea is known to interact or react with a polyalkylene oxide compound to form a crystalline adduct, or "inclusion compound," in which urea molecules are combine with the molecules of the polymer compound in a spiral or helical formation. To achieve this physical arrangement, the polymer compound must have a structure or stereochemistry that will allow it to fit within the spiral of the urea molecules and facilitate occlusion by or with urea. In general, urea will form inclusion compounds with long straight-chain molecules of six or more carbons but not with branched or bulky molecules. Woodworth et al., U.S. Pat. No. 2,675,356, teach detergent compositions manufactured using soaps or other synthetic organic detergents. Woodworth et al. use a urea alcohol complex to form a detergent composition suitable for use and contact with human skin. Shiraeff, U.S. Pat. No. 2,927,900 , teaches solid detergent mass or cake using a normally liquid surface active polyglycol ether detergent component solidified using urea fused with the liquid polyglycol ethers. Gandolfo et al., U.S. Pat. No. 4,265,779, teach grandular detergents containing a suds suppressor composition comprising a liquid hydrocarbon, a nonionic ethoxylate and a compatibilizing agent capable of forming inclusion complexes with the ethoxylate material. The preferred agent in Gandolfo et al. is urea. Hight, U.S. Pat. No. 4,695,284, teaches materials and methods for washing fabrics in cold water comprising built detergent particles containing a nonionic detergent, saturated fatty acid, builder salts, and carriers. A variety of carriers can be used including inorganic carriers such as sodium tripolyphosphate, sodium carbonate, sodium bicarbonate, sodium or potassium chloride, preferred organic carriers include carbohydrates, film forming materials, urea, etc. Materials in Hight are apparently particulate in nature.
To manufacture a solid block urea-based composition, the urea is combined with the ingredients under melting temperatures, commonly referred to as a "molten process," to achieve a homogeneous mixture. The melt is then poured into a mold and cooled to a solid form. For example, U.S. Pat. No. 4,624,713 to Morganson et al. discloses a solid rinse aid formed from a urea occlusion composition that comprises urea and a compatible surfactant, namely a polyoxypropylene or polyoxyethylene glycol compound. The solid rinse aids are prepared by mixing the ingredients in a steam jacketed mixing vessel under melting temperatures and under pressurized steam, heating the mixture to about 220.degree. F., cooling the mixture to about 180.degree. F., pouring the cooled mixture into a plastic container, allowing the mixture to solidify by cooling to room temperature (about 15.degree.-32.degree. C.), and allowing the product to cure or harden for about 2-4 days.
The instability of urea in the presence of alkaline materials is well known. Urea is known to decompose through many intermediate stages into carbon dioxide and ammonia. The decomposition is promoted through increasing alkalinity, the presence of moisture and increasing temperature. Such instabilities have rendered the use of urea, in this art area, an undesirable option as either an active cleaning agent or as a processing or solidification aid in the manufacture of alkaline materials. While urea has found some utility in the manufacture of organic material such as rinse aids and organic detergents as discussed above, the art as a whole did not consider urea a useful alternative in the manufacture of large bulk cast solid alkaline compositions. The presence of any significant amount of an alkaline base including an alkali metal hydroxide, an alkali metal silicate, an alkali metal carbonate, triethanol amine, or other organic or inorganic amines typically resulted in the exclusion of urea as a co-ingredient.
One significant problem that has caused some problems related to the manufacture, storage and use of cast solid alkaline materials relates to the environmental stability of the cast solid. Upon exposure to the atmosphere, alkaline cast solid materials can rapidly absorb substantial proportions of humidity resulting in a softening or dissolution of at least a substantial portion of the cast solid. The absorption of water can result in a softened layer of alkaline material covering the surface of the cast solid block rendering the material difficult to handle and dispense. Further, in conditions of higher humidity or higher concentrations of alkalinity, the absorption of atmospheric humidity can result in the creation of a substantial proportion of a liquid product that can slump or flow from the surface of the cast solid creating a pool of highly caustic material. Not only is the humidity and stability of the material a problem in manufacturing and handling the material, the instability can also cause substantial problems in dispensing. The softened surface or liquid material that can flow from the surface can cause substantial and uncontrollable spikes of material during dispensing. The materials are designed to be dispensed using a spray on type dispenser. In such dispensers, a spray of water is directed onto a surface of the cast solid material. When operating correctly, the spray removes a small portion of the cast solid in the form of an aqueous concentrate which is directed to a warewashing machine. The aqueous concentrate replenishes the concentration of the cleaning agent in the use locus. When the cast solid material is interacted with atmospheric water, the softened surface or the material that flows from the surface of the cast block can introduce an uncontrolled amount of material substantially in excess of that needed to replenish the concentration of cleaning materials in the washing solution. This can result in waste of the cleaning composition, spotting and staining on dishware and other related processing problems.
Accordingly, a substantial need exists to develop methods and compositions that can use urea in the form of an alkaline cast solid material. Further, a substantial need exists in resolving problems related to the humidity instability of cast solid material in manufacture, use and dispensing.